# Non-Reciprocal and Collimated Surface Plasmons in Drift-biased Graphene Metasurfaces

## TL;DR

This paper demonstrates how applying a drift current to graphene metasurfaces induces highly asymmetric, non-reciprocal surface plasmons with potential for unidirectional, collimated, and steerable plasmonic applications across broad frequencies.

## Contribution

It reveals the nonlocal response of drift-biased graphene leading to unidirectional and collimated plasmons, introducing new ways to control surface plasmon propagation.

## Key findings

- Asymmetric dispersion of surface plasmons in drift-biased graphene.
- Highly directive hyperbolic plasmons immune to backscattering.
- Potential for efficient collimation and steering of plasmons using spin-orbit interactions.

## Abstract

We explore the unusual non-reciprocal and diffraction-less properties of surface plasmon polaritons propagating in drift-biased graphene-based metasurfaces. We show that applying a drift-current on a graphene sheet leads to extremely asymmetric in-plane modal dispersions from terahertz to infrared frequencies, associated with plasmons with low-loss (high-loss and ultra-high confinement) traveling along (against) the bias. Strikingly, truly unidirectional wave propagation is prevented by the intrinsic nonlocal response of a graphene, a mechanism that shapes the energy flow over the surface. We also show that highly-directive hyperbolic plasmons completely immune to backscattering propagate obliquely along the drift in nanostructured graphene. Finally, we discuss how spin-orbit interactions can be exploited in this platform to efficiently launch collimated plasmons along a single direction while maintaining giant non-reciprocal responses. Our findings open a new paradigm to excite, collimate, steer, and process surface plasmons over a broad frequency band.

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Source: https://tomesphere.com/paper/1905.10699